O.D. Gonçalves

X-ray scattering from human breast tissues and breast-equivalent materials.

The angular distributions of photons scattered by human breast tissues (adipose and glandular) and by eight breast-equivalent materials (water, polymethylmethacrylate, nylon, polyethylene and four commercial breast-equivalent materials simulating different glandular-adipose proportions) have been measured at a photon energy of 17.44 keV (Kalpha-radiation of Mo). Transmission target geometry has been used with an acceptance of +/- 0.6 degrees and an uncertainty of approximately 7%. Experimental molecular form factors were extracted from diffraction patterns normalizing the number of scattered photons with theoretical data in regions where no structure is expected. Linear attenuation coefficients have been measured for all samples at this energy. The results for water, polymethylmethacrylate, nylon and adipose tissue agree with former reported data. The results for human breast tissues at low and medium scattering angle (1-25 degrees, corresponding to the momentum transfer region between 0.2 and 3 nm(-1)) differ from the breast-equivalent materials. The results for adipose tissue are similar to the corresponding values from commercial breast-equivalent materials while the results for glandular tissue are similar to those for water.

Measurements of photon-atom elastic scattering cross-sections in the photon energy range 1 keV to 4 MeV

Abstract We review the current status of measurements of photon-atom elastic scattering cross-sections for the restricted photon energy range 1 keV up to 4 MeV. Among the key experimental factors which influence the accuracy and precision of a particular type of measurement are the choice of source, detector and scattering geometry. We have examined the interests which motivate the making of measurements, looking at issues at the atomic, molecular and solid state level. Discrepancies have been noted to exist between experiments and between experiments and theory and explanations for these have been sought. It is apparent that over the last fifteen years or so there has been a substantial increase in the number of reported studies of elastic scattering cross-sections for photons of energies

Measurements of X-ray scatter signatures for some tissue-equivalent materials

In this work, we have measured the angular distribution of photons scattered (scattering signature) by five tissue-equivalent materials used in mammography and conventional radiology and four samples used in bone densitometry at the photon energy 17.44 keV using a X-ray tube equipped with a graphite monochromator, a goniometer system and a NaI detector. Results from the tissue-equivalent materials scattering signatures have been compared with previous results for human tissues (adipose, glandular, muscle and bone). The scattering profiles obtained with tissue-equivalent materials are different from those obtained with human tissue. These differences are due to intermolecular correlation on the elastic scattering. Some tissue-equivalent materials present some very sharp peaks, absent in real soft human tissue. These results suggest that a careful analysis of the scattering properties must be done in order to use tissue-equivalent material to simulate human tissues.

Precise evaluation of elastic differential scattering cross-sections and their uncertainties in X-ray scattering experiments

Abstract In this work we propose a method of obtaining elastic scattering differential cross-sections from X-ray scattering experiments with amorphous samples taking into account all background sources and also multiple scattering processes. Background from the ambient and other scattering sources were measured directly. Multiple scattering was calculated through a Monte Carlo code that simulates the actual experiment and may use different theoretical approaches when considering the differential scattering cross-section. The same code, after slight modifications, provides also the attenuation coefficients and the mean scattering angle, which were compared with analytical results. The uncertainty for all experimental quantity was evaluated. As an illustration of the method, the procedure was applied to scattering data obtained for a glandular breast tissue measured inside a cylindrical container.

Modelling the elastic scattering in diagnostic radiology: the importance of structure form factors

The importance of structure form factors in describing elastic scattering in diagnostic radiology was studied through a Monte Carlo code built to reproduce scattering in large water samples. The code, developed by us, considers all relevant interactions, including multiple scattering and interference due to scattering by the liquid structure. Geometrical conditions and energies similar to those found in radiology were used. The secondary to primary radiation ratio using the usual free atom approximation and the structure form factor was obtained and both approaches were compared. Calculations of radiological parameters such as the angular distribution of photons incident on the detector and the fraction of scattered photons stopped by anti-scattering grids were also performed considering mammography, thorax and abdomen radiography conditions. The results have shown that S(beta)/P depends on the experimental set-up, being more important for low momentum transfers and sample sizes for which the multiple scattering is not expected to be significant, as in the case of mammography. It was also verified that large samples increase the probability of multiple scattering, masking the structure peak in S(beta) and making the sample structure important just for relatively thin samples. Considering mammography-like geometry, the maximum of the S(beta)/P distribution considering structure form factors occurs around 15 degrees while the correspondent maximum without considering the structure factors occurs around 10 degrees for any sample thickness. S(beta)/P is almost independent of the irradiation field, with the maximum remaining at 15 degrees and 10 degrees for the SFF and FAFF, respectively. The cases studied in this paper stress some conditions in which it is mandatory to use SFF, but since it requires no further significant efforts, the SFF approach is recommended as a standard procedure when describing the elastic scattering process in radiology.

First experiments on diffraction-enhanced imaging at LNLS.

Diffraction-enhanced images have been obtained using two silicon crystals in a non-dispersive set-up at the XRD2 beamline at the Brazilian Synchrotron Light Laboratory (LNLS). A first asymmetrically cut silicon crystal using the (333) reflection vertically expanded the monochromated beam from 1 mm to 20 mm allowing the imaging of the whole sample without movements. A symmetrically cut Si(333) second crystal was used as a Bragg analyzer. Images of biological samples including human tissue were recorded using a direct-conversion CCD detector resulting in enhancement of the contrast compared with absorption-contrast images.

A Review of Different Lasers in Endonasal Surgery: Ar-, KTP-, Dye-, Diode-, Nd-, Ho- and CO2-Laser

Summary Background and Objective: Endonasal laser surgery is presently performed by seven different laser types with wavelength ranging from about 500 nm to 10.600 nm. It is the purpose of this study to review the clinical applications and to discuss the advantages and problems of each specific laser. Materials and Methods: The interaction of laser radiation and tissue is compared for different laser systems. Clinical applications of endonasal laser surgery are reviewed. Results and Discussions: Absorption and scattering of radiation in tissue depend on the wavelength of the radiation. This has a considerable influence on the radiation field and the temperature distribution during surgery. Different coagulation and evaporation zones arise for each laser system. The study shows that all of these lasers yield good clinical results. This is probably due to the fact that the surgeons properly adapt the power density and the movement of the beam over the tissue.

Accurate Rayleigh differential cross-sections for 60 keV photons. The Ag case

Abstract The angular distributions of the elastic scattering differential cross-section of photons by Cu, Ag, Cd, Pt and Pb (metallic samples) were measured at the Physics Institute of the Universidade Federal do Rio de Janeiro using a HPGe detector and a 241 Am source of 59.54 keV photons. A very careful consideration about error bars was made, improving the confidence in the experimental data. The results were compared with different theoretical calculations of Rayleigh (elastic) scattering, including the results from Pratt and Kissel based on S-matrix theory. As expected, the best agreement between the experimental data and the theoretical results occurs in the comparison with the Pittsburgh calculations, but still some deviations persist. These deviations were not systematic, occurring mainly for silver.

Three-dimensional image construction by curved surface scratches

Scratches on the surface of transparent or nontransparent media reflect, refract, or diffract incident light. Under parallel illumination each length element of a scratch produces a fan beam (in the absence of diffuse scattering). Looking at a curved scratch, the right and left eyes are hit by different fan beams. Thus each eye sees a separate light spot on the scratch, which is the origin of the fan beam. In certain circumstances these spots can be stereoscopically combined by both eyes and only one light spot in space is seen. Three-dimensional images can be created by a large number of such spots originating from circular or semicircular scratches. These scratches can easily be produced on the surface of Plexiglas or other materials by using a compass. Some experiments and the theory of the so-called scratchograms are given. A comparison with holographic images is made.

Angle-dispersive diffraction with synchrotron radiation at Laboratório Nacional de Luz Sı́ncrotron (Brazil): potential for use in biomedical imaging

At low angles the scattering of X-rays in the diagnostic energy range (low-momentum transfer), it is probable that the scattering interaction will be coherent. This coherence gives rise to interference effects resulting in X-ray diffraction patterns that are characteristic of the scattering material. The usefulness of coherent scattering is not limited to crystallography. It can provide information about biological material as well. The interatomic and intermolecular co-operative effects which modify the free-atom coherent scattering process are well known for highly ordered structures such as crystalline materials but are important for amorphous solids and liquids where short-range ordering occurs. X-ray diffraction using synchrotron radiation has became a well established technique. This work introduces a non-destructive synchrotron radiation X-ray diffraction imaging technique. The feasibility of the X-ray diffraction computed microtomography using synchrotron radiation has been investigated. This research was carried out at the X-ray diffraction beam line of the National Synchrotron Light Laboratory supported by the National Council for Scientific and Technological Development (LNLS/CNPq) in Brazil. These experimental patterns were carried out with a 500 microm slit in front of the detector and an 11.101 keV beam (lambda = 1.117 A) monochromatic beam from the double crystal monochromator. The diffracted beam was detected by a fast scintillation detector (10(6) counts s(-1)) designed specifically to meet the needs of high quality X-ray diffraction and synchrotron radiation experiments. The data were recorded at rates of one second per degree of 2theta (angular steps equal to 0.05 +/- 0.01 degrees) and registered by a multichannel analyzer. These experimental data could be used to evaluate the scattering properties of different tissue-substitute (water, lucite, nylon, plastic and polystyrene) and bone-substitute (hydroxyapatite and aluminum) materials. The data are in good agreement with those obtained by other authors, indicating the feasibility of the imaging technique.